#include<stdio.h>
int mySqrt(int x) {
    if (x < 1)return 0;
    int left = 1, right = x;
    while (left < right)
    {
        int mid = left + (right - left + 1) / 2;
        if (mid > x / mid) right = mid - 1;
        else left = mid;
    }
    return left;
}